Wind driven electric power generating devices include one or more rotating blades that move in response to movement of the wind. The blades rotate a shaft at a rotational speed that varies in response to wind speed. The shaft that is directly rotated by the one or more blades of a wind turbine generally rotates at a relatively low velocity. For example, rotation at a rate of 10 to 60 rpm is common for many types of commercial wind turbine generators.
Electrical generators, which are sometimes alternatively referred to as dynamo electric machines, often have an armature or other rotating assembly that preferably rotates at a relatively high rotational speed compared to the rotational speed of the blades when producing electricity. Some common electrical generators preferably operate in the range of 600 to 1,800 rpm. Many types of wind turbine electrical generator systems include a gear box that operates to connect a shaft that is operatively connected to the turbine blades and rotates at the speed thereof, to the electrical generator. The gear box operates to step up the speed from the relatively low speed shaft which rotates at the speed of the turbine blades, and provides an output via one or more relatively high speed output shafts which shaft or shafts are operatively connected to the rotating assembly of a generator and which rotates at a speed that is suitable for the production of electricity.
Wind velocity is often highly variable, irregular and unpredictable. Wind velocity may rise and fall rapidly during gusty conditions. Such repeated rapid changes in wind speed, and the resulting force against the one or more turbine blades of a wind turbine electric generator, may result in excessive torque loading and/or torque spikes in the power transmission system, including the gear box. While the pitch of the blades of the wind turbine may be selectively changeable in many wind turbine electric generator systems, the pitch of the blades is generally not changed rapidly for dynamic or energy production reasons. As a result, blade pitch generally cannot be changed quickly enough to avoid excessive torque that results from wind gusts or highly rapidly varying wind conditions. Rather, systems which control the pitch of the blades will often take considerable time to change the blade pitch sufficiently to reduce torsional load spikes or other undesirable conditions. Many times load spikes, excessive torsional loads and other conditions which can damage components of the wind turbine will have impacted the gear box and other components before a change in pitch can be effective to avoid damage.
Further, when a wind turbine generator is operating efficiently and the generator is applying a resistence load to the high speed output shaft of the gear box, rapid changes in torsional force may be particularly damaging to gears, bearings and other components within the gear box. Such conditions may cause breakage and/or fatigue of shafts and gear teeth, which eventually results in failures of the gear box and connected components. Further in some arrangements, rapid changes in wind speed may cause increases in the rotational speed of the turbine blades and the generator to undesirable levels. Many types of wind turbines are not operated in sustained winds above 55 mph in order to avoid damage to the device components. In cases where the rotational speed of wind turbine blades has reached an undesirable level, a reduction in speed is generally achieved by changing the pitch of the blades. Because in such circumstances the blades and the other system components are rotating at an undesirable high speed, and because of inertial forces, a change in pitch of the blades will often take considerable time to achieve a reduction in the speed of the blades. Thus, considerable time is often required to slow down and/or stop the rotation of the blades.
While some wind turbine electric generator systems include a brake device for stopping and/or preventing rotation of one or more components of the system, such devices are generally configured only to stop and hold one or more shafts against relatively small rotational forces. Such mechanisms will generally operate to prevent the mechanism from rotating once a change in pitch of the turbine blades has been used to slow the rotational speed of the turbine blades. Conventional braking mechanisms cannot generally withstand an extended period of attempting to resist the force of the turbine blades at operating pitch and being rotated by high winds. Further in many conventional arrangements, the braking mechanisms apply braking and holding force on the high speed output shaft of the gear box. As a result, when the brake is engaged, torsional loading and potential gear box wind-up caused by the wind force acting on the wind turbine blades is applied to the gear box. Such conditions may cause fatigue and/or damage to internal gear box components as the gear box resists the torsional loading.
Wind turbine electric generators and related systems may benefit from improvements.